This change only updates strings and adds RPC aliases, but should simplify the
implementation of address labels inhttps://github.com/bitcoin/bitcoin/pull/7729, by getting renaming out of the
way and letting it focus on semantics.

The difference between accounts and labels is that labels apply only to
addresses, while accounts apply to both addresses and transactions
(transactions have "from" and "to" accounts). The code associating accounts
with transactions is clumsy and unreliable so we would like get rid of it.

For non-RPC changes, this is true, but for RPC commands backported from Core, it's directly relevant, as businesses with patches or special infra to handle ABC not supporting expected RPC commands in Core can now migrate since they know the behavior is now the same/similar.

This would benefit from being just one list. If we have enough items that we need categories, we'll make category. Catogories should be done based on what users will want to dig (change in the RPC API, change in build dependencies, new wallet features, new mining feature, etc...) rather than the source.